The present invention relates to a sliding member of excellent friction and wear characteristics.
Since polytetrafluoroethylene (hereinafter simply referred to as "PTFE resin") has excellent self-lubricating properties and low friction coefficient, as well as has chemical resistance and heat resistance, it has been used generally for sliding members such as bearings.
However, since the sliding member composed only of the PTFE resin is poor in the abrasion resistance and creep resistance, such a drawback is compensated, for example, by (1) incorporating a solid lubricant such as graphite and molybdenum disulfide, and/or a reinforcing material such as glass fibers and carbon fibers to the PTFE resin, or (2) filling and covering the PTFE resin in the mesh and on the surface of a metal mesh, depending on the application use of the sliding member.
The sliding member formed by the method (2) has been known, for example, in Japanese Patent Publications No. 55-23740 and No. 53-35107, and Japanese Patent Application Laid-Open (KOKAI) No. 63-57919.
Japanese Patent Publication No. 55-23740 discloses a self-lubricating lining foil comprising a metal wire fabric, a fluoro-plastic and a reinforcing material of inorganic fiber.
Japanese Patent Publication No. 53-35107 discloses a covering sheet as a bearing material, comprising a metal mesh and a fluoro polymer sintered therewith, in which crossing wires portions of the metal mesh are welded at intersections to each other.
In the technique disclosed in Japanese Patent Publications No. 55-23740 and No. 53-35107, a metal mesh is used as a substrate, and a fluoro polymer incorporated with a reinforcing filler is filled and covered in the mesh or on the surface of the metal mesh.
Japanese Patent Application Laid-Open (KOKAI) No. 63-57919 discloses a sliding bearing material comprising a matrix composed of 5 to 25% by volume of lead, 10 to 50% by volume of glass fibers, 40 to 80% by volume of polytetrafluoroethylene and 10 to 50% by volume of zinc sulfide or barium sulfate having a particle size within a range from 0.1 to 1.0 .mu.m, and an expanded metal of 0.3 to 0.9 mm in thickness composed of malleable aluminum alloy having elongation at break of 8 to 20% and Brinnel hardness of 35 to 65, covered therewith, in which rhombic openings of the expanded metal are filled with the matrix and a frictional sliding layer of 0.01 to 0.3 mm in thickness composed of the matrix is present on the expanded metal.
In the technique disclosed in Japanese Patent Application Laid-Open (KOKAI) No. 63-57919, an expanded metal is used as the substrate, and polytetrafluoroethylene incorporated with a reinforcing filler is filled and covered in the mesh and on the surface of the expanded metal.
The sliding members described above exhibit low friction coefficient and satisfactory performance in various different working conditions, for example, under dry condition, oil-immersed condition or oil-lubricated condition, but can not be said to have sufficient durability of the sliding member because the resin layer forming a sliding surface is a thin film.
Further, in a PTFE resin composition for sliding member, as fillers for engineering plastics, particularly, graphite, molybdenum disulfide or other metal sulfides, metal oxides, and inorganic fibers such as glass fibers and carbon fibers may be used.
However, although these fillers contribute to the improvement of the abrasion resistance of the resin layer, the fillers bring about a problem of worsening the low frictional properties inherent to the PTFE resin unless a sufficient care is taken for the blending amount.
As a result of the present inventors' earnest studies, it has been found that by filling and covering a resin composition in the mesh and on the surface of a metal mesh, in which the resin composition is produced by blending a reinforcing filler such as glass fibers, phosphate and barium sulfate and, optionally, solid lubricant at a predetermined ratio to the PTFE resin, the thus obtained sliding member exhibits excellent sliding characteristics and durability.